Crucial factors affecting the physicochemical properties of sol–gel produced Fe3O4@SiO2–NH2 core–shell nanomaterials

Multifunctional nanomaterials with task-specific physicochemical properties, especially core–shell nanostructures with Fe 3 O 4 core and NH 2 -functional shells (Fe 3 O 4 @SiO 2 –NH 2 ), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol–gel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe 3 O 4 @SiO 2 –NH 2 nanomaterials with magnetic response core, NH 2 -functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol–gel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe 3 O 4 @SiO 2 –NH 2 materials. The TEOS pre-hydrolysis and the critical time (around 90 min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28 mmol L −1 in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe 3 O 4 @SiO 2 –NH 2 magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core–shell structure (~200 nm in diameter), relatively large BET surface area (~138 m 2 /g) and high incorporation of amino-functionality (~2.90 wt %).